Config: Add "execName" to specify ini and rgssad filenames

mkxp.conf.sample

@@ -256,6 +256,19 @@
 # SE.sourceCount=6
 
 
+# The Windows game executable name minus ".exe". By default
+# this is "Game", but some developers manually rename it.
+# mkxp needs this name because both the .ini (game
+# configuration) and .rgssad (encrypted data archive) must
+# carry the same name minus their extension, and we cannot
+# guess the executable's name.
+# You could just as well rename them both to "Game.ini" and
+# "Game.rgssad", but specifying the executable name here
+# is a tiny bit less intrusive.
+#
+# execName=Game
+
+
 # Give a hint on which language the game title as
 # specified in the Game.ini is, useful if the encoding
 # is being falsely detected. Relevant only if mkxp was